Dear user, You haven t mentioned how long this has been happening, though you said several days which I take to be 5-7 days. I would presume this is a viral infection, because with GERD, you are unlikely to get a recurrence if it has already subsided a year ago. Also, he would not have a foul-smelling stool. I recommend that his parents continue feeding him with smaller quantities of milk or food more frequently, use a vomiting medicine like domperidone or ondansetron (they might need to go to a doctor for prescriptions of the above) and give him water with salt and sugar to prevent dehydration. If the symptoms aren t better in a day or two, please ask the parents to take the kid to his doctor.